Methods of Trench Excavation

B.S. 1911 OTSIXVOP1 .i ui .r.N'o.is 1 oimAay Digitized by the Internet Archive in 2013 http://archive.org/details/methodsoftrencheOObern METHODS OF TRENCH EXCAVATION BY Louis Stewart Bernstein THESIS FOR THE degree of Bachelor of Science IN CIVIT. ENGINEERING IN THE college of engineering UNIVERSITY OF IEEINOIS 1911 UNIVERSITY OF ILLINOIS May 25, 1911 I recommend that the thesis prepared under ray supervision by L0UI3 STEWART BERNSTEIN, entitled Methods of Trench Excavation^ be approved as fulfilling this part of the requirements for the degree of Bachelor of Science in Civil Engineering. Instructor iry^fivil Engineering Recommendation approved:: Head of the Department of Civil Engineering." 1S754Q t r . OUTLINE Introduct ion 1. Ordinary Manual Excavating. 2. Excavation "by Drag Scrapers. 3. Excavation by Stea:ai Shovels. 4. Excavation by Trend: Machines. 5. Conveying Machines. 6. Miscellaneoun Machines & Methods. INTRODUCTION. The o"oject of this article is to compare the different methods used in excavating trenches of differing sizes and cross sections, and in most cases the approximate cost with these methods. Since the sizes of trenches vary in v/idth and depth from a few inches to several feet it can easily he seen that entirely different methods must he used to excavate economi- cally. In fact, a minute study of the different methods, and of the existing conditions in the country where the work is to he done . must he made "before the material can he excavated with the "best financial results. There are really two classes of trenches, namely, those that are needed in municipal work for sewer drains and water lines, an" those that are needed for irrigation and transportation. A discussion of the methods applied to hoth classes will he made. In extensive work of the second class ordinary excavation by hand labor is almost worthless and for this reason special machines and devices have been adopted, the ohject of these "being to :- 1. Improve the method and rapidity of excavation. 2. Reduce the cost of the work. 3. Reduce the lahor troubles which generally attend the work especially where large gangs of men are employed seme distance from the lahor centers. In the following article, a "brief description of the various methods will he given. 2 EXCAVATING SY HAND. On nearly all small jobs it is more economical to use hand labor for excavating than to use excavating machines. The reasons for this are obvious. The cost and time taken for hauling and setting up the trenching machine is large in comparison to the cost of excavat ing^and to avoid this unnec- essary expense and delay hand labor is preferable. The di- viding line between hand and machine excavation can. be on!/ det ermined by the existing conditions such as size of the job, labor conditions, and experience. The principle of hand excavation is nearly always the same. The line of the trench is generally given by cen- ter or side stakes. These stakes sometimes give the cut to the desired grade. A strong white line is then stretched along the sides of the trench to the desired width and the sides are marked by a pick or spade. The laborers are then placed at regular intervals, varying from six to twenty feet, in single line except where the trend" is eight or more feet in width. In this case they are placed in a double line and work together in pairs. Each man, or pair of men, lv then assigned a certain section and unless conditions are unusual they are supposed to finish the assigned section in a certain time, generally one half or one day. The advantage of this arrangement is obvious, as the foreman can easily note the progress of the men by merely observing the depth of the cut. In this way the good and the inefficient workers can easily be determined. It is conceded to be good practice to place 3 an experienced ditcher alongside one of less experience to act as a pace maker, as the tendency will be to hasten the progress of the poorer man. Since the men or laborers are usually of different nationalities, a good foreman is necessary to keep peace and harmony between the men. The foreman should be a man who understands human nature as well as trenching and he should be physically able to enforce order if necessary. As before stated a common method of determining the depth of the cut is with grade stakes at the side of the trench. These stakes are generally placed about fifty feet apart and the foreman merely places a rod in the trench to check the cut wheh the desired grade is reached. When the grade is parallel to the surface of the ground a stick with the desired cut marked upon it is all that is necessary tc use, to see that the men dig to the required grade. Another common method of determing the desired cut is as follows: Stakes are driven at each end of the trench and to these stakes a strong chalk line is tied so that the c^alk line has exactly the same grade as the trench. A stick, long enough to reach both the bottom of the trench and the chalk line, is then used to see if the required depth is reached. If the trench is true to grade, the stick will touch the line and trench bottom at all points. This is a very popular method and is used extensively by many contractors. The earth first excavated should be thrown to what will be the outside edge of the bank, since it cannot be thrown there when the trench deepens without extra handling. Up to a depth of nine feet , the earth can be thrown to the surface in 4 one handling, although extra men are required to pile it on the side of the trench. Then the depth exceeds nine to twelve feet, it is necessary to handle the material twice "before it reaches the surface. A platform or staging is "built about six or seven feet "below the surface onto which the earth is thrown "by two to four men and from here it is generally thrown to the surface "by one or two men. If the depth is greater than 16 or 18 feet , another platform about seven to eight feet below the first is necessary to handle the dirt. making three handlings before the dirt reaches the sur- , face. The process is then as follows. "Four men, if the trench is wide enough, throw the dirt to the second platform; from here it is handled by two men who throw it to the first platform and one man shovels it to the surface. The cost of ditching this way is very expensive as seven mer: are really doing four men's work. It is also necessary to make the trenches wider than usual to allow the men enough room in which to work. The platform consists of short pieces of plank placed crosswise of the trench, their ends resting on the rangers; or of long pl&nks lengthwise of the trench resting on the braces. The latter method is the better of the two especially for wide trendies. If cross platforms are used they should be staggered so that the right side of one is directly over the left side of the other, making the alternate platform vertically above each other. If longitudinal bracing is used, the successive tiers should be placed alternately upon the opposite sides of the trench. Those platforms should never contain more than two men so as to keep them busy at all times. 5 When the trench has "been dug to the desired grade and the pipe laid,, the excavated material is replaced "by throw- ing It in. Frequently little attention is given the hackfill. This is had practice as the soil shrinks and large settlements are caused^ To prevent this as much as possihle, the earth should "be tamped when replaced and even then small settlements will he noticed. If care is taken with the hackfill, these settlements can he greatly reduced and the result will he a "better grade of work. Too much stress can not he lftid upon this, and the contractor should he made to t&ke as much care with the hackfill as with the trench itself^ especially so on work in which the trench is laid in a city street If there is any paving on the street, the paving material should he kept apart from the excavated material as the former must 'he replaced with as much care as possihle. It is good policy to keep the picks and shovels used in good con- dition. For this purpose there should he fully twenty-five to one hundred percent more picks and shovels than workmen. For digging the round pointed shovel is hest , hut staging men can work much faster with square pointed shovels. There should also he a supply of long handled shovels hut these should not he used except where the shoveling is both deep and easy The Municipal Engineering and contracting Company, of Chicago, have prepared a tahle showing the cost of hand excavation in comparison to machine excavation. The first part of the tahle will he given on the following page while the second part will he given in the article on Fxcavation hy ., » Trenching Machines. The following table has "been "based on easy spading earth and has assumed that the men can excavate and throw back ten yards per day which can only he done under the best of conditions.

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